This invention relates to skylights, for example, of the general type disclosed in U.S. Pat. No. 4,548,006, No. 4,549,379 and No. 4,823,525 which are owned by the assignee of the present invention, and the disclosures of which are incorporated by reference. In such skylights, it is common to construct a wood rectangular frame-like curb which projects upwardly from a sloping roof deck. The curb may also be constructed by vacuum-forming a sheet of thermoplastics material with an outwardly projecting integral peripheral flange or flashing portion, such as disclosed in connection with FIG. 3 of above U.S. Pat. No. 4,549,379. A skylight unit is mounted on the curb and commonly includes one or more spaced flat panes of glass surrounded by a rectangular aluminum trim frame, and sealant strips are used between the lower glass pane and the supporting surface of the curb and also between the glass panes and the surrounding trim frame. The skylight unit may also be constructed of one or more panes of transparent plastics material, and the panes may be dome-shaped with the upper or outer pane including an integral depending skirt which surrounds the curb unit, as also disclosed in above U.S. Pat. No. 4,549,379.